SEOUL — North Korea has stockpiled enough weapons-grade uranium for six nuclear bombs, amid growing concerns it could be primed for another nuclear test, an expert claimed Wednesday.

The South Korean nuclear expert told the Yonhap news agency that Pyongyang appeared to have started relying on enrichment activities because of its dwindling stock of plutonium after two rounds of nuclear tests.

In November 2010, North Korea revealed its uranium enrichment plant to US scientist Siegfried Hecker, claiming it was being used for energy development. The plant was thought to have been operational in 2009 – meaning it could have produced enough enriched uranium for up to six bombs.

The South Korean expert, who was not named, said, “If the North Korean claim is true, it could allow the North to make some 88lbs (40kg) of highly enriched uranium per year, enough for one or two atomic weapons.”

Last month, a failed long-range rocket test drew condemnation from the UN Security Council. The test, which saw the rocket break up and fall into the sea off the Korean peninsula, was widely thought to be a disguised attempt to try out banned long-range missile technology.

Previously unsuccessful launches in 2006 and 2009 were followed by the testing of plutonium devices in North Korea, Yonhap said.

The expert said South Korea estimated its neighbor spent at least $6.58 billion on its nuclear weapon program.

The country is under UN sanctions for missile and nuclear testing in 2009 and could face further sanctions after the April 13 failed launch.